Vectors based on adeno-associated viruses have shown promise for achieving stable gene expression following in vivo gene transfer. AAV infections appear to be endemic in humans based on seroepidemiologic studies. Only one of the six known serotypes of AAV was recovered from human biological material with the other serotypes isolated as contaminants of laboratory stocks of adenovirus preparations. Several issues have emerged in the application of AAV vectors for human gene therapy. The efficiency of gene transfer achieved with vectors based on the known serotypes is insufficient for many applications envisioned by Projects 2 and 3 of this P01, which aim to target heart and liver, respectively. In addition it would be useful to know more about the biology of natural infections with AAV in designing safe and effective gene therapy strategies. In preparation for this competing renewal we undertook a series of studies to address these points by evaluating non-human and human primates for endogenous AAVs. These preliminary studies led to the discovery of novel families of primate AAVs and suggested a mechanism for creating diversity based on homologous recombination. The goal of this project is to provide to Projects 2 and 3 the vectors and biology necessary for them to develop promising gene therapy approaches for cardiovascular diseases based on gene transfer to heart and liver, respectively. The Specific Aims of Project 1 are as follows: The first Specific Aim will evaluate a limited number of novel AAV pseudotypes for gene transfer to liver and heart. These studies will include an evaluation of gene transfer efficiency, stability of transgene expression, toxicity, immunity, and serology. The second Specific Aim will study the mechanisms by which AAVs undergo recombination. The third Specific Aim will characterize the molecular status of endogenous AAVs and their interactions with vector DNA following gene transfer.